MIT explains why bad habits are hard to break

Habitual activity--smoking, eating fatty foods, gambling--changes neural activity patterns in a specific region of the brain when habits are formed. These neural patterns created by habit can be changed or altered. But when a stimulus from the old days returns, the dormant pattern can reassert itself, according to a new study from the Massachusetts Institute of Technology, putting an individual in a neural state akin to being on autopilot.

"It is as though, somehow, the brain retains a memory of the habit context, and this pattern can be triggered if the right habit cues come back," Ann Graybiel, the Walter A. Rosenblith professor of neuroscience in MIT's Department of Brain and Cognitive Sciences, said in a statement. "This situation is familiar to anyone who is trying to lose weight or to control a well-engrained habit. Just the sight of a piece of chocolate can reset all those good intentions," Graybiel said.

The neural patterns get established in the basal ganglia, a brain region critical to habits, addiction and procedural learning. In Graybiel's experiments, rats learned via specific cues that there was chocolate at one end of a T-shaped maze. While the rats were still learning, their basal ganglia neurons chattered throughout the maze run. That's because in the early stages, the brain seeks out and soaks in information that could prove important.

As the rats learned to focus in on guiding cues (in the experiment, an audible tone that guided them toward the chocolate), the behavior of the neurons changed. They fired intensely at the beginning and the end, but remained relatively quiet while the rats scurried through the maze.

Subsequently, the reward was removed. While the audible cue became meaningless, everything in the maze from beginning to end became relevant again. The neurons fired throughout the run. But when the reward reappeared, the pattern of beginning and ending spikes separated by downtime reappeared.

Sound familiar?

Graybiel speculated that the beginning and ending spike patterns reflect the nature of a routine behavior. Once initiated, individuals essentially know what to do next. Excitement returns when the reward appears. While the neural patterns can be created through voluntary activity, this sort of pattern also appears in certain disorders. Parkinson's patients, for instance, have difficulty starting to walk, and obsessive-compulsive people have trouble stopping incessant behavior.

Ideally, the research will help scientists come up with new techniques for more firmly changing habitual or addictive behavior.

A more full report will be published in the Oct. 20 issue of Nature. The National Institute of Health and the Office of Naval Research supported the research.